But what if you're a smaller shop, consisting of 1-5 Drupal experts? You obviously can't afford to hire someone full-time to work on Drupal Core development -- but you can still reap benefits from contributing some of your own time, or (if you have employees) paying them for a few hours a week to contribute to Drupal Core or another Drupal sub-project (module, theme, etc.) that many people use, or volunteering in another way (providing free training in your local area, organizing a Drupal meet-up, etc.). The main benefits I see:

Your own expertise in Drupal will grow, making you a better Drupal shop.

Your reputation among members of the international Drupal community will grow, possibly leading to concrete benefits, such as referrals.

Your reputation among members of your local Drupal community will grow, almost certainly leading to greater possibility of referrals and project partnernships, which a small company always needs.

When a client is looking for a Drupal contractor to hire, the fact that you are a contributor to the Drupal project or the organizer of a local meeting may tip the balance towards you over another Drupal shop. (A little marketing is in order: publicize your contributions on your web site, and make sure, when talking to clients, to mention your work -- it will add to the sense of expertise that a prospective client is looking for.)

And if your company doesn't have time to contribute volunteer hours to the Drupal project, you can also reap some benefits (good will in the community and good feelings from clients) by contributing financially (again, if you do a little marketing). I know of several great ways to do this:

Join the Drupal Association, the non-profit that does so much for the Drupal open-source project (such as paying for the servers that drupal.org and associated sites run on). Once you become a member, you can display a DA badge on your web site.

Donate regularly to Drupal developers via Gittip -- you could donate to the Drupal Core team or to one or more developers that works on key modules that your company uses. Once you start donating, you can display a Gittip badge on your web site.

Fund particular Drupal projects via Drupalfund, a crowdsourcing platform specifically for Drupal projects. Unlike Gittip, which is meant to be used for weekly contributions to individuals and teams, Drupalfund is for one-time contributions to particular projects (adding features to a module, porting a theme to a new Drupal version, etc.).

So... Pick your method, and do something to help the open-source project that your livelihood depends on!